1. Field of the Invention
The present invention relates to an attitude angle control apparatus which controls an attitude angle of a predetermined part of a marine vessel, such as the attitude angle of the hull, the attitude angle of a propeller, or the attitude angle of the propeller relative to the hull. More particularly, the present invention relates to an attitude angle control apparatus that improves the specific fuel consumption of the marine vessel.
2. Description of the Related Art
It has been known that, for example, by properly adjusting the attitude angle of a propeller (outboard, inboard/outboard, inboard, or waterjet) attached to a small craft, it is possible to reduce hull resistance, and consequently improve the specific fuel consumption of the small craft.
However, to improve the specific fuel consumption, it is necessary to adjust the attitude angle on a continuous basis by detecting subtle changes in engine speed and attitudes caused by ever-changing weather and hydrographic conditions. This places a heavy burden on the navigator. Thus, in many cases, even a skilled navigator makes only a few adjustments during a voyage. As for novice navigators, they mostly navigate with resistance set to the highest level, i.e., with the propeller placed closest to the marine vessel's transom (full trim-in).
In view of the above-described problems, various methods have been proposed to improve the specific fuel consumption by reducing hull resistance.
For example, an invention disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 9-76992) proposes a method in which the manufacturer determines a relationship between the attitude angle of a propeller and the specific fuel consumption experimentally in the development phase before shipment and retains the relationship data in the form of a map in an electronic control unit (ECU), allowing an appropriate attitude angle to be selected according to navigational conditions.
An invention disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 61-12498) proposes a method which involves fine adjustment of the attitude angle of an outboard device when the marine vessel is traveling at a fixed throttle setting and selecting the attitude angle which maximizes marine vessel speed as an optimum attitude angle. The maximum marine vessel speed means the minimum hull resistance, and thus means that the attitude angle which maximizes specific fuel consumption can be selected. Since this method determines the optimum attitude angle by measuring the relationship between attitude angle and marine vessel speed during navigation, it can be applied to any combination of a hull and outboard device.
An invention disclosed in Patent Document 3 (U.S. Pat. No. 5,785,562) proposes a method which involves fine adjustment of the attitude angle of a propeller equipped with a device which allows the marine vessel to travel at a fixed engine speed and selecting the attitude angle which minimizes the fuel consumption as an optimum attitude angle. This method can be applied to any combination of a hull and propeller as is the case with the invention disclosed in Patent Document 2.
However, according to the invention disclosed in Patent Document 1, a hull and propeller need to be selected together when conducting experiments in the development phase. Consequently, the hull and propeller are selected and provided as a pair, which limits the types of equipment that can be mounted in the marine vessel.
Also, the inventions disclosed in Patent Documents 2 and 3 involve measuring marine vessel speed and fuel consumption at each attitude angle during navigation and selecting the attitude angle which provides the best marine vessel speed and fuel consumption, but measurement on the water is prone to great error due to disturbances such as winds and waves, unlike measurement on land. Thus, long hours of measurement are required to check the effects of attitude angles accurately.